Circuit breaker



C. THUMIM CIRCUIT BREAKER June 24, 1952 3 Sheets-Sheet 1 Filed Jan. 7. 194'? INVENTOR.

Car-I Tburmm C. THUMIM CIRCUIT BREAKER Juhe 24, 1952 3 Sheets-Sheet 2 Filed Jan. 7. 194'? INVENTOR.

.CcU"| Tbumlm AT TORN E Y5 June 24, 1952 c THUMIM 2,601,422

CIRCUIT BREAKER Filed Jan. 7, 194'! 3 Sheets-Sheet 3 INVENTOR. Carl Tbumvm WW6 v- M ATTORNEYS Patented June 24, 1952 UNITED STATES PATENT OFFKJE' CIRCUIT BREAKER Garli Thum m, eadon, a si hor o I; E:

Circuit Breaker Company, Philadel hia, I?a-., av corporation of Pennsylvania rplic -ion-.-l n riy 7, 194.7, S rial. N0.- 720,555;

8'Glaims. 1

My invent on. rel te to. r u t break s, an more particularly to circuit breakers which utilize the electromagnetic acticnof currentinthe controlled circuit for closing the breaker as well as f oropening the breaker.

Heretofore. c rcu t reak rs have b n d si so that a. 110.09 s, formed. in he cir u t path rough, he breaker such hat s o t. u t urrent flow ng Sets up. a ma ne field h a ds he. on ningsprins n p et n -them v e r to, in posit on. Th kno n as. e owoff, effect.

In ma y ns nces t s lso. d s bl d r n the clo in op a on. o the ci uit k t se ure.- rst he e se e i e n m y a o QB." efi ct o, have he ma n e ndueed y c rren n the ent lled' c r it drive the con a s l sed- T s ens r s oo o c on closing in cases where the breaker may, be closed" against excessive current or short circuit conditions, avoids chattering and freezing at the contacts due to poor contact. engagement, and p rmi s promp pp inr on o short cuit conditions.

A novel blow-n, blow-oh type ofcircuitbreilker is described in application ofgJoseph D Wood', Serial No. 6 45 118, filed February 2; 1946, now abandoned, and assigned to the assignee of' the present invention,

A specific object of my, invention is the arrangement of a blow-closed; blow-open circuit breaker wherein the blow-open effect is utilized entirely by itself to? result in, the rapid opening of the contactson tripping, and wherein no auxiliary means suchas tension springs or compres.' sion springs are utilized to open the circuit breaker.

in accordance with my invention, I; provide one pivot for the movable arm during closing and a different pivot for opening. The pivot during closing is such that at the instantthe circuit contacts engage (but before closing movement is completed) the electromagnetic forces setup by the currentin the circuit are such as to drive the movable arm, through its remaining small move ment to efiect complete closure or contact en: gagementr Thereafter during tripping in response to abnormal current conditions in the controlled; ci 1:-. Qui t vot s sh so. th t h ma et c fi d nd cedi y e r nt ai s n. dr v n h movable arm to itsopen position.

D e t app xima e y U-sh ed c n guration of he. tu n con ac s, of: most circuit breakers, high electromagnetic forces are im- 2 no ed pon. t e r e Parts enfa u r nt. i epmtcximately 0.000. a nere r mo e ro gh. he. cir uithe e forcesb em tremely h w th r t. lue re ches 1. 0 mpe e. nd h on ons h o ces may reach several; thousandpounds.

To withstand these forces, the stationary parts must be made; extremely strong and*rlgld. This can usually be done without too Inuchdiiliculty. The movable parts oft the breaker gi s the most difliculty. Many contact arrangements have been devised to construct flexible contacts so that the electromagnetic forces increase contact pressure,

as for instance shown in- Patent No. 2,514,839; issued J uly I1, 1950,. These constructions are necessary so that the breaker may remain closedandso that the contact will open in the proper sequence during the opening stroke; even in the presence of high short circuit current.

In most circuit; breakers, the, moving contact forms substantially the bottom section of the U shaped; configuration of 'the circuit breaker and opens outwardly awax from the two legs ofthe U-shape. In this arrangement theefiectof the electromagneticforces is to force the moving contacttowards the open position Thi aids high speed openin under fault conditions and aids circuit, interruption" but it; pre-' sents a real; anddifilclllt problem when the break-- er is required to be; closed against a short circuit. In fact manyof the present commercial circuit breakers admittedly willnot close against a short circuit equal to their interrupting capacity much less against a current value equal to their nionrentary rating or the asymmetrical, inrush' cur; rent thatoccurs in the first half cycle on an A. 0; short circuit.

In an electrically operated circuit breaker; the electrical operating mechanism is required to function properly over a, specified range of con;- trol voltage. For instance, a, D. C: closing mechanism is required to close the breaker from 90' volts to volts, at the closing mechanism; This represents a wide range and; is about as much as canbe expected. Breakers that just close on thelow voltage will slam closed-= on thc high: voltage: with. so. much energy that there is danger Off. breaking parts; even, at no load; and without consideration of the; for es imposed: by

short circuit current. The solution. theprob=- 1cm doesnot lie; making: bigger and stronger closing; mechanism. whichwillr have power enough to force the breaker to;theclosedpositioninvtlie 3 closing at no load over this wide range of control voltages.

I have solved the problem by providing a novel circuit breaker in which the electromagnetic forces imposed are balanced out during closing stroke or by properly proportioning the parts so that these forces actually assist in closing the breaker and provide faster and more positive closing in the presence of a high short circuit current.

The operation of my novel circuit breaker when closing, over the control voltage range, is practically the same whether it carries large or small amounts of current. That is to say, the breaker operates effectively for all values of current over the entire range up to its interrupting rating, because my novel invention employs the natural electromagnetic forces to assist in the operation of closing.

However, when the breaker is opening, my invention contemplates using the electromagnetic forces in such a way as to assist this opening operation and cause the breaker to open faster in direct proportion to the magnitude of the current in the system. It should also be noted that when closing against a short circuit, no electromagnetic blow-open force is imposed on the moving arm since no current is flowing until the contacts touch; the full electromagnetic blowopen force is then instantly present.

The relatively balanced arrangement of the magnetic forces involved in my novel circuit breaker avoids the necessity of attempting to match the closing force of the breaker mechanism against the magnetic forces present in the closing arm when carrying high currents.

In general, my invention contemplates a construction in which one arm, which pivotally carries a second contact carrying arm, is arranged to have a blow-open effect thereon in response to a fault current, but is normally prevented from operating in response to such blow-open effect by a latch arrangement thereof. The contact car rying arm which is pivotally mounted on the first arm has a blow-closed action which is operative to effect engagement of the contacts and a resultant blow-closed action only while the first arm is in its latched condition and unable to operate in response to blow-open action.

I thus take advantage of both a blow-closed action for closing the contacts and a blow-open action which becomes effective when the fault currents effect disengagement of the latch of the first arm.

It is thus an object of my invention to utilize the short circuit or fault current itself to aid in the closing of the contacts of the circuit breaker.

It is another. object of my invention to so arrange the contacts of a circuit breaker that the blow-closed effect of the electrical and magnetic forces around the contacts will be such as to drive the contacts together when the circuit breaker is closed.

It is another object of my invention to so arrange the contacts that even though a blowclosed effect is achieved when the circuit breaker is closed, a blow-open effect is nevertheless achieved during the opening operation of the circuit breaker.

The foregoing and many other objects of my invention will become apparent in the following description and drawings in which Figure 1 is a schematic side view of my novel circuit breaker contact arrangement showing the circuit breaker contacts closed.

Figure 2 is a View corresponding to that of Figure 1 showing the contacts tripped open, butbefore the latches are re-set.

Figure 3 is a view corresponding to those of Figures 1 and 2 showing the circuit breaker open, with the latches reet and prepared to close.

Referring now to the figures, I have here shown my novel circuit breaker it! which is so arranged that during the closing movement and just as the contacts engage, but before they have fully engaged, the current loop through the elements provides a blow-closed effect. When the circuit breaker is tripped in response to fault currents, the elements are so arranged that the current loop provides a blow-open effect and the stationary contacts I! are of the blow-closed construction.

The circuit breaker i is supported in any suitable manner on a panel ll, carrying the additional supporting bracket 22 and front panel l3.

The back panel H carries an upper back connection stud l5 and a lower back connection stud l6 mounted in any suitable insulator H5 and H6. The upper back connection stud carries at the end thereof a stationary contact structure ll comprising an arcing contact l3 and a main stationary contact if]. The arcing and main contacts [8 and [9 are supported in any suitable manner in the contact housing H and are biased toward current carrying relation with the movable contact elements by the compression springs 20, 21. They are so arranged in any of the well known methods so that the electro magnetic force due to high short circuit current will tend to force them into better contact engagement with the moving contacts 45 and 46.

The movable contact arm assembly has an upper arm 26 and a lower section 21 on opposite sides of the pin 50, the arm being pivoted on the pin 50. The movable contact arm 25 is supported by pin 50 on the lower arm 33 which in turn is pivoted at pin 30 on the extension 3| of the lower back connection stud l8.

Pigtail connection 32 between lower end of section 27 of arm 25 and lower back connection stud l6 and 3! completes the circuit.

The current path established when the contacts are closed is thus from the upper back connection stud l5 to the stationary contact structure ll, including the arcing contact I8 and the main contact 19, then through the movable arcing contact 55 and the movable main contact 46 to the contact arm 25 and through pigtail 32 to the lower back connection stud 16.

Contact arm 25 is held in the closed position by the toggle 52 comprising links 53 and 54 and the knee pin 55. Link 53 may be of insulating material in some cases. Link 53 is pivotally connected to pin of upper arm 25 and at its opposite end is connected to knee pin 55. Link 54 is connected at one end to pin 55 and at its opposite end is pivoted on the pin 57 mounted between the sides of bracket 60 which in turn is supported on the front panel I 3.

Link 54 has an angular extension 62 so that members 54 and 52 form a bell crank lever around the pin 57. The outer or lower end of extension 62 carries a latch roller 63 which is engaged by the latching notch 64 of the pivoted latch member 65. Latch member 65 is in the form of a bell crank lever rotatably mounted on the pin 65 carried between the sides of bracket 60.

The eccentric stop. 98- cooperates with the. extension 52 of the link 54 in order to keep the latch roller 63. close. to the latching notch 64. and prevent the linkage. 52 from. riding under center.

The upper arm 58. of the latch lever 65 is in the pathof movement of the armature Hi of fault current trip coil H. When the trip coil H is energized in response to predetermined circuit conditions, the armature 1:0 is, driven to the left to rotate the arm 58 and hence the latch member:B5.in counterclockwise direction to release the latching extension 64 ofthe latch 65. from, the latch roller 6.3 of the bell crank levers 54 and 62..

Since the toggle 53 5.5e5 is broken slightly upwardly in the closed position of the circuit breaker, the contact arm may now, on release of the latch roller 63, rotate clockwise on pin 31, resulting in the further breaking upwardly or collapse of the toggle 52; that. is, the entire systemv consisting of contact arm 25 and the supporting arm 33 moves outwardly during theopeningor tripping, movement ofthe circuit breaker around the pin 35,

A portion of the link 54 strikes the buffer 75 carried by bracket 56 and the upward breaking of thetoggle 52 and hence the opening movement of contact arm 26; is thereby limited.

The closingarm 85 which maybe of insulating material is connected at one end to the pin 28 at the lower end of contact arm, 25 and at the, opposite end to a pin 8] on the armature 52 of the closing solenoid 8 3, The armature 8-2 is normally biased toward the left by the compres sion spring 85 which is seated atone end in the recess 86 of armature 82 and atthe opposite end in the recess 81 of the housing 88 for the coil 83. Housing 88 is supported from the front panel l3.

With the circuit breaker in the open position, the compression spring 85 as seen in Figure 3 has moved the armature 82 fully to the left, thus moving the closing arm 83, and the pin 28 to the left, and rotating the lower section 21 of the contact arm 25 clockwise around the pin 50.

In thefully closed position of the circuit breaker, (Figure 1) the energization of the closing coil 83 has attracted the armature 82 to the right, compressing the spring 85 and pulling the arm 80 and pin 28 to the right, and rotating the lowor section 21 of contact arm 25 counterclockwise around the pin 50. When the closing movement is completed, the arm 80 is latched in closed position as shown in Figure l, by the latch roller 9ll inthe latching detent SI of the arm 88.

Latch roller 90 is supported at the end of the bell crank latching lever 92, which latching lever is rotatably supported on the pin 93 carried by an extension 94 of bracket 60. The upper arm 95 of latching lever 92 is so arranged that during; the opening movement of the circuit breaker, that is, when the circuit breaker moves from the position of Figure 1 to the position of Figure 2, the latch roller 63 at the end of arm 54-52 will strike the upper end 95 of the latch lever 92, as seen in Figure 2, to rotate the latching lever 92 counterclockwise and to move the latch roller 90, out, of. the latching detent 9|, of closing arm 80, so that the. closing. arm 80 may move to the left in response to the bias of compression spring 85, as shown in Figure 3.

Tension spring 95 connected between the arm 95 0f the latching lever 92 and extension 91 of the latching lever 65. biases the latching lever 92 tQWfllfd; clockwise rotation and hence toward latching position with respect to arm 80, and; at

the same time biases the. latching lever- 65 toward clockwise rotation and interengagement with the latch roller 53. The single tension spring 96 isv thus used to re-set both of the latch-. ing levers 65; and 92.

Thus, as previously described, on a. tripping of the circuit breaker, the armature l0 rotates latch lever 65 counterclockwise to release the latch roller 63. and to permit the toggle 52 to. break upwardly so that the arm 25: may rotate clockwise toward opening position. Th-isis. the initial step which occurs. during tripping and is shown in Figure 2. i

As the toggle 52 breaks upwardly, roller- 5-3 strikes the upper arm 95 of the latching lever $2, rotating the latching lever 92 counterclock-r wise and lifting the latch roller 8.0 out, of the latching detent 91. The arm 89. is. now. free to move in response to. the bias of the compression spring 85. and moves to. the. left carrying the pin 28 with it and rotating the lower section, 21 of the contact arm 25 clockwise.

As the arm 80. moves to the left, the; pin 28 which extends slightly beyond the arm 21: en.-. gages the arm 3-3 and rocks it counterclockwise about the pivot 58., thus extending the tog le 52 to the position shown in Figure 3. In thisposiw tion the toggle. 52 has been extended until. the pin 63 engaged and rolled over the latch 64 until the pin 63 re-seated itself in the latch 64.. In. the final movement of the latch under action of the spring 95, a slightly further extension of the toggle 52 is effected and the movable contact is now in position for re-closing.

In the closing operation (Figure 3) the en.- ergization of the closing coil 83 attracts the armature 82 to the right against the bias of compression spring 85 pulling the arm 80 to. the right and hence rocking the pin 28 to the right and thus pivoting the arm 25 around the, pivot 55. On completion of the closing movement of arm 88:, roller 90 drops. into detent ill. under the influence of spring 95.

The operation whereby a blow-closed effect is secured during closing and in the closed condition of the circuit breaker and a, blow-open; effect is secured during tripping. willv now be described,

With the circuitbreakerin the closedposition. shown in Figure 1, the magnetic forces set up by currents flowing in the loop described; above act on the pin 50 and tend to rotate. arm 33 clockwise about its pivot 30, but this force is.

counteracted by the latched condition of the circuit breaker since this force is applied through the pin 50 on the toggle 52 at this time latched against movement. The magnetic forces; also act on thecontact arm 25, part of the forces act,- ing on the section 21- and tending to rotate it counterclockwise about, pivot 50 and a portion acting on the section 26 and tending to rotateit clockwise about the pin 50. Inasmuch as; the section 21, is longer than the section 26, the net force is a counterclockwise action blowing the contacts into closed engagement as desired.

If now. a fault current flows in the line protected by the circuit breaker, the relay 10. connected in series in the circuit will be energized by these fault currents and operate, its plunger '10 to the left to engage and rock the bell crank arm 68 in a counterclockwise direction about its pivot 65 against the action of the spring 9 5. The bell crank will thereupon disengage the pin 63 thereby releasing the toggle 52 which will; collapse upwardly due to the forces applied. thereto through the; pin 50 acting on the arm- 33.

For an instant thereafter, the blow-closed action due to the difference in length between the arms 26 and 27 will effect good contact engagement between the contacts as the arm 33 moves about its pivot 36, thus slightly lowering the pin 28 and maintaining the arcing contacts in engagement 45-18.

On the collapse of the toggle, the pin 63 strikes against the lever 95 and rocks the bell crank 9592 in a counterclockwise direction against the bias of the spring 96 until the pin 90 is withdrawn from the notch 91. This frees the arm 80 which now operates under the action of the spring 85 to move to the left, rocking the arm 26-41 in a clockwise direction about its pivot 50 and this, together with the movement of the arm 33, completes the disengagement of the contacts with a blow-open action, it being understood that the blow-open force at the pin 50 is considerably greater than the net blow-closed action between the arms 26 and 21.

The contacts now move to complete disengaged position shown in starting operation in Figure 2 and completed in Figure 3. As soon as the arc has been interrupted by the are extinguisher mechanism shown schematically above the contacts, the plunger 10 is restored to its normal position and the bell crank 68 is rocked in a clockwise direction about its pivot 65.

The movement of the arm 80 to the left in rock- As a result of this operation of the arm 80,

member 21 is rocked in a counterclockwise direction about its pivot 50 and the arcing and main contacts are re-engaged in the usual manner.

During re-engagement and before the roller 90 has dropped into the notch 9|, the blow-closed action is effected. During this time it will be noted that although upon engagement of the contacts against a fault current a blow-open action is produced against the arm 33, this arm 4 is latched against movement whereas the contact carrying arms 21 and 26 are movable about their pivot 50 so that the resultant blow-closed action due to the greater length of arm 21 with respect to arm 28 is such as to blow the contacts into engagement as is desired in order to ensure good contact during the engaged period.

On completion of the closing operation, the roller 90 drops into latch 9| to latch the con tacts closed. If, however, following the blowclosed action and engagement of the contacts, the fault current is such as to re-energize magnet H, the above described tripping operations with the effective blow-off action will be repeated.

Thus I have provided a construction which ensures good blow-closed action during closing and while the circuit breaker is closed, and at the same time secured effective blow-open action in the event of a tripping of the circuit breaker in response to the fault currents. Attention is directed to related application Serial No. 720,561, filed January 7, 1947.

In the foregoing I have described my invention in connection only with a specific illustrative embodiment thereof. Since many variations and modifications of my invention should now be obvious to those skilled in the art, I prefer to be bound not by the specific disclosures herein contained, but only by the appended claims.

I claim:

1. In a circuit breaker for protecting an electrical system, said circuit breaker having a movable contact and a cooperating contact, a movable contact arm assembly carrying said movable contact on one end thereof and comprising an upper arm and a lower section, a first pivot, a lower arm pivotally mounted at one end on said first pivot, a second pivot on the other end of said lower arm, said assembly being pivotally mounted on said lower arm on said second pivot, a latch member for maintaining said second pivot fixed, a closing arm connected to said lower section, means for biasing said closing arm to rotate said assembly in a direction to move said movable contact out of engagement with said cooperating contact, a latch for latching said closing arm against action by said biasing means, the circuit of the system being protected extending through the cooperating contact and the movable contact assembly back to the system forming a loop, the magnetic forces set up by currents flowing in the loop acting on said lower section and tending to rotate said lower arm about its first pivot to move the movable contact to disengage said cooperating contact, the magnetic force being counteracted by the latched condition of said second pivot, said magnetic forces also acting on said assembly, part of said force tending to rotate said upper arm about said second pivot to move said movable contact out of engagement with said cooperating contact and part of said force tending to rotate said lower section about said second pivot to drive the movable contact into closer engagement with said cooperating contact, said lower section being longer than said upper arm to produce a resultant force driving the contacts into engagement with each other, an electromagnet responsive to fault current in the circuit being protected for opening said latch member, said movable contact arm assembly being thereupon responsive to the magnetic forces of said fault currents to rotate said lower arm on said first pivot and to rotate said assembly to move said movable contact out of engagement with its cooperating contact, means responsive to the disengagement of said contacts for opening said latch, said closing arm thereupon acting in response to the action of its biasing means to operate said assembly further in a direction toward contact disengagement, said closing arm in its operation under action of said biasing means operating said latch member to latching position for maintaining said first pivot fixed, and means for operating said closing arm against said biasing means to rotate said assembly about said second pivot to effect contact engagement of said fixed and movable contacts.

2. In a circuit breaker for protecting an electrical system, said circuit breaker having a movable contact and a cooperating contact, a movable contact arm assembly carrying said movable contact on one end thereof and comprising an upper arm and a lower section, a first pivot, a lower arm pivotally mounted at one end on said first pivot, a second pivot on the other end of said lower arm, said assembly being pivotally mounted on said lower arm on said second pivot, a latch member for maintaining said second pivot fixed, a closing arm connected to said lower section, means for biasing said closing arm to rotate said assembly in a direction to move said movable contact out of engagement with said cooperating contact, a latch for latching said closing arm against action by said biasing means, the circuit of the system being protected extending through the cooperating contact and the movable contact assembly back to the system forming a loop, the magnetic forces set up by currents flowing in the loop acting on said lower section and tending to rotate said lower arm about its first pivot to move the movable contact to disengage said cooperating contact, the magnetic force being counteracted by the latched condition of said second pivot, said magnetic forces also acting on said assembly, part of said face tending to rotate said upper arm about said second pivot to move said movable contact out of engagement with said cooperating contact and part of said force tending to rotate said lower section about said second pivot to drive the movabl contact into closer engagement with said cooperating contact, said lower section being longer than said upper arm to produce a resultant force driving the contacts into engagement with each other, an electromagnet responsive to fault current in the circuit being protected for opening said latch member, said latch member being effective to maintain said second pivot fixed during the closing operation of said assembly while said lower section is moved about said second pivot and said latch maintaining the lower end of said assembly fixed during circuit opening operation while said latch member is reclosed to permit opening movement of said arm about said first pivot.

3. In a circuit breaker for protecting an electrical system, said circuit breaker having a movable contact and a cooperating contact, a movable contact arm assembly carrying said movable contact on one end thereof and comprising an upper arm and a lower section, a first pivot, a lower arm pivotally mounted at one end on said first pivot, a second pivot on the other end of said lower arm, said assembly being pivotally mounted on said lower arm on said second pivot, a latch member for maintaining said second pivot fixed, a closing arm connected to said lower section, means for biasing said closing arm to rotate said assembly in a direction to move said movable contact out of engagement with said cooperating contact, a latch for latching said closing arm against action by said biasing means, the circuit of the system being protected extending through the cooperating contact and the movable contact assembly back to the system forming a loop, the magnetic forces set up by currents flowing in the loop acting on said lower section and tending to rotate said lower arm about its first pivot to move the movable contact to disengage said cooperating contact, the magnetic force being counteracted by the latched condition of said second pivot, said magnetic forces also acting on said assembly, part of said force tending to rotate said upper arm about said second pivot to move said movable contact out of engagement with said cooperating contact and part of said force tending to rotate said lower section about said second pivot to drive the movable contact into closer engagement with said cooperating contact, said lower section being longer than said upper arm to produce a resultant force driving the contacts into engagement with each other, an electromagnet responsive to fault current in the circuit being protected for opening said latch member, said lower arm being movable about said first pivot during opening of said circuit breaker contacts and said assembly being movable about said second pivot during closing operation of said circuit breaker.

4. In a circuit breaker for protecting an electrical system, said circuit breaker having a movable contact and a cooperating contact, a movable contact arm assembly carrying said movable contact onone end thereof and comprising an upper arm and a lower section, a first pivot, a lower arm pivotally mounted at one end on said first pivot, a second pivot on the other end of said lower arm, said assembly being pivotally mounted on said lower arm on said second pivot, a latch member for maintaining said second pivot fixed, a closing arm connected to said lower section, means for biasing said closing arm to rotate said assembly in a direction to move said movable contact out of engagement with said cooperating contact, a latch for latching said closing arm against action by said biasing means, the circuit of the system being protected extending through the cooperating contact and the movable contact assembly back to the system forming a loop, the magnetic forces set up by currents fiowingin the loop acting on said lower section and tending to rotate said lower arm about its first pivot to move the movable contact to disengage said cooperating contact, the magnetic force being counteracted by the latched condition of said second pivot, said magnetic forces also acting on said assembly, part of said force tending to rotate said upper arm about said second pivot to move said movable contact out of engagement with said cooperating contact and part of said force tending to rotate said lower section about said second pivot to drive the movable contact into closer engagement with said cooperating contact, said lower section being longer than said upper arm to produce a resultant force driving the contacts into engagement with each other, and an electromagnet responsive to fault current in the circuit being protected for opening said latch member.

5. In a circuit breaker for protecting an electrical system, said circuit breaker having a movable contact and a cooperating contact, a movable contact arm assembly carrying said movable contact on one end thereof and comprising an upper arm and a lower section, a first pivot, a lower arm pivotally mounted at one end on said first pivot, a second pivot on the other end of said lower arm, said assembly being pivotally mounted on said lower arm on said second pivot, a latch member for maintaining said second pivot fixed, a closing arm connected to said lower section, means for biasing said closing arm to rotate said assembly in a direction to move said movable contact out of engagement with said cooperating contact, a latch for latching said closing arm against action by said biasing means, the circuit of the system being protected extending through the cooperating contact and the movable contact assembly back to the system forming a loop, said lower arm rotating about said first pivot for effecting disengagement of said contacts and said assembly rotating about said second pivot for effecting engagement of said contacts.

6. In a circuit breaker for protecting an electrical system, said circuit breaker having a movable contact and a cooperating contact, a movable contact arm carrying said movable contact,

a pivot for said movable contact arm, a latch mechanism for maintaining said pivot fixed, a closing mechanism connected to said movable arm for operating said arm about said pivot to efiect contact engagement of said movable and cooperating contacts, the length of said movable arm on one side of said pivot with respect to the length on the opposite side of said pivot being such that the electromagnetic forces set up by short circuit currents tend to drive said contacts into contact engagement, electromagnetic means responsive to fault currents in the circuit being protected by said circuit breaker for opening said latch, said pivot being thereupon free to move, and means responsive to the electromagnetic forces caused by said fault currents for operating said pivot and said movable arm to effect contact disengagement between said movable and cooperating contacts.

7. In a circuit breaker for protecting an electrical system, said circuit breaker having a movable contact and a cooperating contact, a movable contact arm carrying said movable contact, a pivot for said movable contact arm, a latch mechanism for maintaining said pivot fixed, a closing mechanism connected to said movable arm for operating said arm about said pivot to effect contact engagement of said movable and cooperating contacts, said movable arm having a section on one side of said pivot longer than the section on the other side of said pivot, the electromagnetic forces due to current flowing in said circuit breaker acting on said longer section to assist said closing mechanism in driving said contacts into engagement, electromagnetic means responsive to fault currents in the circuit being protected by said circuit breaker for opening said latch, said pivot being thereupon free to move, a second pivot for said contact arm and means responsive to the electromagnetic forces caused 1 by said fault currents for operating said movable arm about said second pivot to effect contact disengagement between said movable and cooperating contacts.

8. In a circuit breaker for protecting an electrical circuit, a first connection stud, a second connection stud, said first connection stud supporting a first contact, a pivot, a movable contact arm mounted on said pivot and having a short first section carrying a moving contact for cooperating with said first contact, said arm also having a long second section, an electrical connection from said moving contact arm to said second connection stud, said connection stud moving contact arm and electrical connection forming a loop with said electrical circuit, the electromotive forces due to fault current flowing in said circuit breaker exerting less force on said first section than on said second section of said moving contact arm, means for moving said moving contact arm about its pivot from circuit open position to contact engaging position, a latch for normally maintaining said pivot fixed while said closing means is moving said contact thereabout, and means responsive to fault current in said circuit breaker for opening said latch to permit said movable arm and pivot to move to effect disengagement of said contacts.

CARL THUMIM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,123,282 Harris Jan. 5, 1915 1,560,440 Tritle Nov. 3, 1925 2,025,697 Baker Dec. 24, 1935 2,212,732 Fisher Aug. 27, 1940 2,227,160 Seaman Dec. 31, 1940 2,275,891 Cox et a1 Mar. 10, 1942 2,295,307 Thumim Sept. 8, 1942 2,545,341 Caswell Mar. 13, 1951 

